The first time you compare an offer letter ($85,000) to a real paycheck ($2,580 every two weeks), the math feels off. Twenty-six pay periods at $2,580 is $67,080. Where did the other $17,920 go?
The short answer is: federal income tax, two payroll taxes, state income tax in most states, and pre-tax deductions you may have opted into. The longer answer is what this guide is about: not how to file a return, but how a salary turns into a take-home number, and why two people earning the same gross can end the year owing very different amounts.
If you want to skip the explanation and just see a number, the US Income Tax Calculator will give you an estimate based on your filing status and income. For the paycheck-by-paycheck view, the Paycheck Calculator is the one that mirrors what shows up on a pay stub.
Gross, taxable, and net are three different numbers
Three terms get used interchangeably and shouldn't.
Gross income is what your offer letter says. It's the total compensation before anything is taken out.
Taxable income is what's left after subtracting deductions the tax code allows, most commonly the standard deduction, plus pre-tax contributions to a retirement plan, certain health plans, and a few smaller items. The federal tax brackets are applied to this number, not your gross.
Net income (your take-home) is what hits your bank account after federal income tax, Social Security, Medicare, any state and local income tax, and any post-tax deductions like Roth contributions or insurance premiums that aren't pre-tax.
The chain runs: gross → minus pre-tax deductions → taxable income → tax owed → minus tax → minus payroll taxes → minus other withholdings → net pay. Every link in that chain answers a different question.
The standard deduction does most of the work
Most filers do not itemize. They take the standard deduction, which is a flat amount the IRS lets you subtract from gross income before the brackets get applied. The amount depends on filing status (single, married filing jointly, head of household) and updates each year for inflation.
The mechanic is simple. If you are single and earn $70,000 in gross income with no other adjustments, you don't pay federal income tax on the full $70,000. You subtract the standard deduction first, and the brackets apply to the smaller remaining number.
Itemizing, claiming the actual dollar value of mortgage interest, state and local taxes paid (subject to limits), charitable donations, and certain medical expenses, only beats the standard deduction when those line items add up to more than the standard amount. For most renters and most homeowners with modest interest, the standard deduction wins.
There are also above-the-line adjustments that reduce income before you even get to the deduction step. The most familiar are traditional 401(k) contributions through payroll, Health Savings Account contributions, and certain self-employed retirement plan contributions. These reduce taxable income dollar-for-dollar. That is different from a credit, which reduces tax owed, but powerful in its own way.
How marginal brackets actually work
This is the part where most people get confused, and once you see it, it doesn't unconfuse easily without help.
The US federal income tax is progressive and marginal. The current bracket structure (for 2025, applied to 2026 returns) has seven federal rates: 10%, 12%, 22%, 24%, 32%, 35%, and 37%. The exact dollar thresholds where each rate kicks in depend on filing status and adjust annually for inflation. The IRS posts the current schedule each year.
"Marginal" means the rate applies only to the income inside a given bracket, not your entire income. If your taxable income lands you in the 24% bracket as a single filer, you do not pay 24% on every dollar. The first slice of income gets taxed at 10%. The next slice at 12%. The next at 22%. Only the income above the 24% bracket threshold is taxed at 24%, and only up to the next threshold.
A made-up example with simple numbers:
Imagine three brackets: 10% on the first $10,000 of taxable income, 20% on the next $30,000, and 30% on anything above $40,000.
For someone with $50,000 of taxable income:
- 10% of the first $10,000 = $1,000
- 20% of the next $30,000 = $6,000
- 30% of the last $10,000 = $3,000
- Total federal tax = $10,000
That person is "in the 30% bracket" but they paid $10,000 on $50,000, an effective rate of 20%. The real US brackets are more granular and the rates are different, but the mechanic is identical.
The Tax Bracket Calculator is a quick way to see which brackets a given taxable income would touch and how much falls into each one. It's a useful sanity check before any conversation about a raise or a side income.
Marginal versus effective rate
Two numbers describe how much tax you're paying, and they tell different stories.
The marginal rate is the rate that applies to your next dollar of income. It matters when you're deciding whether a raise, a bonus, or a side gig is worth chasing; only the new income above your current bracket threshold is taxed at the higher rate.
The effective rate is your total federal tax divided by your taxable income (or sometimes by gross income, depending on the source). It tells you the average bite the federal system took.
For most middle-income households, the effective rate sits well below the top marginal rate that shows up on the paystub. A single filer with $90,000 of taxable income might be in the 22% bracket but have an effective federal income tax rate closer to 15%, because the 10% and 12% brackets shielded the first chunk of income.
Federal income tax is not the only thing coming out of your paycheck
Two payroll taxes also leave the paycheck on the way to your account.
Social Security tax is currently 6.2% of wages, up to an annual wage base limit (the limit updates each year). Once your year-to-date wages cross that limit, Social Security tax stops being withheld for the rest of the year.
Medicare tax is 1.45% of all wages, with no cap. A higher additional 0.9% kicks in on wages above a threshold for single and married-filing-jointly filers.
Together, those are usually called FICA, and employers pay a matching amount on their side that you don't see on your stub. If you're self-employed, you pay the combined rate yourself, called the self-employment tax: same total, just visible on a different form.
On top of federal tax and FICA, most states impose their own income tax. A few states don't, which is a real reason two people with the same gross salary can take home very different amounts depending on where they live. State tax is layered on after federal calculations and isn't covered in detail here, but it can easily account for a few thousand dollars a year in either direction.
A worked paycheck example
Take a single filer in a state with a roughly 5% flat state income tax, earning $72,000 a year, contributing 5% of pay to a traditional 401(k), with no other adjustments.
Annual gross: $72,000 Traditional 401(k) (pre-tax): –$3,600 Taxable wages for federal income tax: $68,400
Apply the standard deduction (using a stylized $14,500 amount for illustration): taxable income of about $53,900.
Federal income tax (using the simplified bracket example earlier, which is not the real US bracket schedule; see the IRS for current figures): roughly $7,400.
FICA:
- Social Security at 6.2% of $72,000 = $4,464 (the 401(k) doesn't reduce FICA)
- Medicare at 1.45% of $72,000 = $1,044
- FICA total = $5,508
State income tax at 5% of $68,400 = $3,420.
Estimated annual take-home: $72,000 – $3,600 – $7,400 – $5,508 – $3,420 ≈ $52,072, or about $2,003 every two weeks.
The numbers shift significantly with filing status, state, deductions, and credits. The point is the structure: pre-tax items reduce federal taxable income, the standard deduction reduces it further, the brackets apply to that final taxable number, and FICA and state run on parallel tracks based on their own rules.
The US Income Tax Calculator handles the federal piece using current-year brackets. For the per-paycheck breakdown, the Paycheck Calculator handles FICA and a simplified state estimate. The Salary Calculator is handy when you're comparing offers or converting between hourly, weekly, and annual figures before any tax calculation.
Withholding versus your actual tax
A surprise on April 15, whether a big refund or an unexpected bill, usually comes from a mismatch between what your employer withheld during the year and what your actual return calculates.
Your employer estimates withholding based on the W-4 form you filled out and the IRS's tables. It's an estimate. If your real situation differs (a side gig, a second household income, large investment income, a major life change), the withholding can be too high or too low. A large refund means you over-withheld. A bill means you under-withheld. The IRS calls under-withholding by enough an "underpayment" and may charge a small penalty.
The fix is usually a fresh W-4. The form has changed a lot in the past several years and now asks more directly about second jobs and dependents instead of using "allowances." Updating it after a job change, marriage, divorce, a new child, or a meaningful side income generally avoids most surprises.
What a calculator can and cannot do
A general US income tax calculator is great for estimating federal tax liability on a straightforward W-2 income. It is much less useful, and easy to misread, for the following:
- Multiple W-2 jobs, each with its own withholding
- Significant 1099 / self-employment income
- Equity compensation (RSUs, ISOs, NSOs)
- Investment income, capital gains, qualified dividends
- Itemized deductions versus the standard deduction
- Tax credits like the Child Tax Credit, the Earned Income Tax Credit, education credits, and the saver's credit, each with their own eligibility rules
- Alternative Minimum Tax in certain higher-income or equity-heavy situations
- State and local income tax detail
For most of those, a calculator gives a starting estimate at best. Filing software or a tax professional is the correct next step.
Common mistakes
Confusing the bracket with the rate. Being "in the 24% bracket" doesn't mean 24% of your income disappeared to federal tax. The effective rate is almost always lower.
Treating pre-tax contributions as free money. A traditional 401(k) reduces taxable income today, but the withdrawals are taxed later. A Roth contribution uses after-tax money but the qualified withdrawals are tax-free. They're trade-offs, not freebies.
Forgetting state tax. Two states with the same gross income can produce different take-home pay by thousands of dollars. State rules change too.
Assuming a bonus is taxed at a higher rate. Supplemental income (bonuses, commissions) is often withheld at a higher withholding rate as a default, but the actual tax liability is calculated on your total income at year end. Excess withholding comes back as a refund.
Treating the calculator as the filing return. A calculator estimates. The actual return reconciles everything: credits, deductions, capital gains, the works. Use one to plan; use a return (or a preparer) to file.
Practical scenarios
A recent graduate earning $48,000 with no 401(k) and no other adjustments will typically see a federal effective rate in the low single digits to low double digits, plus FICA, plus state if applicable. Most of the tax pressure comes from FICA, not federal income tax, at that income.
A married couple earning $185,000 combined with two children may end up with a much lower effective federal rate than expected, because the Child Tax Credit reduces tax owed dollar-for-dollar after the bracket math runs. Credits change the picture more than people anticipate.
A high earner with $240,000 of W-2 wages plus $40,000 of RSU income should expect the brackets to stack, because RSUs are usually taxed as ordinary income at vesting, and should expect the additional Medicare surcharge to start showing up. A tax estimate based only on the W-2 will undershoot.
FAQs
Why is my paycheck smaller than my salary divided by twelve? Federal income tax, FICA (Social Security and Medicare), state income tax in most states, and any pre-tax or post-tax deductions you signed up for. The first time you see the breakdown, the FICA portion in particular is often larger than expected.
Does being in the 24% bracket mean I pay 24% on everything? No. Brackets are marginal. Only the income above the 24% threshold is taxed at 24%. The earlier brackets still apply to the earlier income.
What is the difference between a deduction and a tax credit? A deduction reduces taxable income, so it saves you taxes at your marginal rate. A credit reduces tax owed dollar-for-dollar. A $1,000 credit beats a $1,000 deduction at any income level.
Are payroll taxes the same as federal income tax? No. FICA (Social Security and Medicare) is a separate set of taxes from federal income tax. Both come out of the paycheck, but they fund different things and follow different rules.
Why is my withholding different from my final tax bill? Withholding is an estimate based on the W-4 you filed. The actual tax bill is what your return calculates. Updating the W-4 after major life or income changes keeps the two close.
Should I itemize or take the standard deduction? Whichever is larger. Most filers come out ahead taking the standard deduction. Homeowners with significant mortgage interest, large state and local tax payments (within limits), substantial charitable giving, or major medical expenses are the most likely to gain from itemizing.
Related guides
- UK Income Tax Explained: PAYE, National Insurance, and Real Take-Home Pay
- Canada Income Tax Explained: Federal, Provincial, and Take-Home Pay Basics
- India Income Tax Explained: Old Regime vs New Regime in Simple Terms
This article is educational. Tax law and bracket thresholds change every year, and individual situations vary widely by state, filing status, deductions, credits, and income type. The IRS website is the authoritative source for current rules. For decisions, talk to a qualified tax professional.